1. Field of the Invention
This invention relates to a method of measuring the battery level in a mobile telephone. The term ‘mobile telephone’ used in this patent specification should be expansively construed to cover any kind of mobile device with communications capabilities and includes radio telephones, smart phones, communicators, and wireless information devices. It includes devices able to communicate using not only mobile radio such as GSX or UMTS, but also any other kind of wireless communications system, such as Bluetooth.
2. Description of the Prior Art
It is desirable to monitor the battery level in a mobile telephone for various reasons. For example, users need to be presented with an accurate indication of battery charge level whilst the phone is in ordinary use so that the phone can be re-charged in a timely manner. Similarly, users need to know how effective charging up has been to tell if further charging is required. However, conventional battery charge level measurement techniques have significant problems. For example, the voltage of a battery can be measured during charging to give an indication of the battery charge level. However, batteries typically approach their maximum voltage within 10 minutes of charging, even though a full charge may take 60 minutes or more, so that a battery charge level indicator just measuring battery voltage will be very misleading. There is a pressing need for a more accurate method of measuring battery levels during charging.
A mobile telephone typically presents to the user a graphical indication of the state of the battery charge level: for example, there could be an image of a battery, divided into 4 segments. When no segments are permanently displayed, then the battery is low. When all segments are displayed, the battery is full. Generally, for a given segment to be displayed, the voltage delivered by the battery must exceed a given voltage threshold. Hence, for a 4 segment display, there would be 3 voltage thresholds.
Whilst a mobile telephone is in normal use (e.g. in idle mode or in actual communication), conventional battery level measurement techniques, based upon measuring voltage levels, are more accurate. However, one complicating factor is that these voltage thresholds conventionally differ depending on whether the telephone is in idle mode, or is in communication, or is charging. Ensuring that the correct threshold voltage value is used in the battery level computation adds complexity to conventional systems. Moreover, measured battery voltages are very noisy due to the complexity of a cellular system and specific filtering is needed to get reliable information.